Fluid valves are often used in process control plants or systems to control the flow of process fluids. In general, fluid valves typically include a valve trim assembly or apparatus that includes a valve plug (e.g., a metal valve plug) and a valve seat (e.g., a metal seat ring) that are disposed in a fluid path to control the flow of fluid through a passageway between an inlet and an outlet. A valve stem or shaft operatively couples the valve plug to an actuator such as, for example, a pneumatic actuator, a manual actuator, etc. The actuator moves the valve plug between an open position at which the valve plug is spaced from the valve seat to allow fluid flow through the passageway and a closed position at which the valve plug sealingly engages the valve seat to prevent fluid flow through the passageway.
In severe service applications such as, for example, in the petrochemical industry, control valves may be subjected to severely erosive fluid conditions that can rapidly wear or reduce the operating life of the valve trim (e.g., a valve seat, a valve plug, etc.). For example, the valve trim may be exposed to flowing process fluids that contain entrained particulate (e.g., ceramic catalyst fines). Valve seats and/or valve plugs made of ceramic materials are often employed in severe service applications to reduce damage and/or wear caused by severely erosive process fluids that may otherwise damage metallic valve seats and/or valve plugs, thereby increasing the operating life of the valve seat and/or valve plug.
Although ceramic valve seats and/or valve plugs are highly resistant to the above-noted erosive or corrosive effects of particulate and the like, contaminates or material such as particulate (e.g., entrained particulate catalyst) and/or or relatively high viscosity fluids may adhere to the sealing or seating surfaces of the valve plug and/or the valve seat as the valve plug sealingly engages the valve seat. Such contaminates or material may prevent the sealing surface of the valve plug from sealingly engaging with the seating surface of the valve seat, thereby causing fluid leakage across the valve seat when the valve is in a closed position.